Thread: finding radius of a circle - please help!

could anyone quickly help me find this radius...i am totally stuck here and have to know this before i can move forward.

Find the standard form of the equation -

center is (8, 3) and passes thru (-6, -1)


so far i have figured out (x-8)^2 + (y-3)^2 = r^2

the radius is what i cannot understand what to figure out...

Use the distance formula:

Yes, you're on the right track. Now all you have to do is... Substitute and into the same equation to get .

I hope that helps.

ILoveMaths07.

Originally Posted by shipwreck

could anyone quickly help me find this radius...i am totally stuck here and have to know this before i can move forward.

Find the standard form of the equation -

center is (8, 3) and passes thru (-6, -1)


so far i have figured out (x-8)^2 + (y-3)^2 = r^2

the radius is what i cannot understand what to figure out...

The radius of a circle is by definition, the distance from the center to any point on the circle. What is the distance from (8, 3) to (-6, -1)?

Another perfectly good way to do this is to say that, since (-6,-1) is ON the circle, it must satisfy that equation. If x=-6 and y= -1, what does your equation give you?